The match cannot continue unless the blood is controlled. Usually players will be given a chance to go to the bathroom and wash a bit of the blood off (you do not want blood dripping all over the place and what not) and then just make it so that the nose stops gushing out blood and if anything, stick a tissue up the nose and play like that.
Was there any incident registered in the history something like this???
As for the tournament rules, i think tournament doctors can't treat the concerned person having injury or anything of that sort.
Any serious injury happened in the tournaments so far??